Method of screening a color picture tube

ABSTRACT

THE SCREEN OF A COLOR PICTURE TUBE IS PROVIDED WITH AN INTERLACED PATTERN OF FILTER COMPONENTS INDIVIDUALLY TRANS MISSIVE OF ONE OF THE PRIMARY COLORS, GREEN, BLUE AND RED THE FILLERS ARE APPLIED THROUGH A PHOTOGRAPHIC PRINTING PROCESS IN WHICH THE PROCESS FOR DEVELOPING ANY NE OF THE THREE FILTER COMPONENTS EMPLOYS A COATING OF BOTH A METALLIC LUSTER AND A PHOTOSENSITIVE RESIST. THE FILTER COMPONENTS ARE DIMENSIONED TO OVERLAP AT THEIR PERIPHERAL PORTIONS AND DEFINE, IN THE AREAS OF OVERLAP, A LIGHT ATTENUATOR. THE NON-OVERLAPPING PORTION OF EACH FILTER RECEIVES A DEPOSIT OF A PHOSPHOR WHICH EMITS LIGHT OF THE WAVELENGTH TO WHICH THE ASSOCIATED FILTER COMPONENT IS TRANSMISSIVE.

April 10, 1973 R. c. ROBINDER 3,726,678

METHOD OF SCREENING A COLOR PICTURE TUBE Filed Aug. 24, 1970 I I I I l linventor Ronald C. Robinder A'ufrney United States Patent 3,726,678 METHOD OF SCREENING A COLOR PICTURE TUBE Ronald C. Robinder, Hanover Park, Ill., assignor to Zenith Radio Corporation, Chicago, Ill. Filed Aug. 24, 1970, Ser. No. 66,457 Int. Cl. G03c 5/00, 7/00, 1/6'6 US. Cl. 9636.1 5 Claims ABSTRACT OF THE DISCLOSURE The screen of a color picture tube is provided with an interlaced pattern of filter components individually transmissive of one of the primary colors, green, blue and red. The filters are applied through a photographic printing process in which the process for developing any one of the three filter components employs a coating of both a metallic luster and a photosensitive resist. The filter components are dimensioned to overlap at their peripheral portions and define, in the areas of overlap, a light attenuator. The non-overlapping portion of each filter receives a deposit of a phosphor which emits light of the wavelength to which the associated filter component is transmissive.

CROSS REFERENCES TO RELATED APPLICATIONS The subject invention is a further development of the process of screening described and claimed in copending application Ser. No. 830,288, filed June 4, 1969', in the name of Howard G. Lange, now Pat. No. 3,569,761. Closely related but specifically difi'erent screening processes are described and claimed in the following applications filed concurrently herewith: Ser. No. 66,455 of Irwin Kachel and Ser. No. 66,454 of Ghulam A. Khan.

BACKGROUND OF THE INVENTION The present invention is directed to the screening of color picture tubes and is of general application.

Customarily, the screen of a color picture tube has deposits of different phosphor materials which, in response to excitation by the impacting electrons of a scanning beam, emit light of wavelengths corresponding to the primary colors green, blue and red. These phosphors are distributed over the screen in an interlaced recurring pattern and ma have any of a variety of configurations but usually are in the form of dots or stripes. The process of this invention is useful irrespective of the specifics of the phosphor deposit but, for convenience, particular attention will be addressed to processing the screen of a picture tube which is of the mosaic type, that is to say, is composed of a multiplicity of dot triads with each triad consisting of a dot of green, a dot of blue and a dot of red phosphor material. The triads are distributed over a field constituting the image reproducing area and it too may have different configurations such as round or rectangular. The rectangular field is the more popular and will be assumed for the screens discussed herein.

As described in US. Pat. 3,114,065, issued Dec. 10, 1963 to S. H. Kaplan, distinct advantages may be realized through the association of filter components with the phosphor deposits of color tubes. structurally, by way of illustration, a filter element may be interposed between each phosphor deposit and the faceplate of the tube with the filter element highly transmissive to the wavelength of light emitted by the phosphor when excited but otherwise serving substantially as a light attenuator.

This same general concept is extended in the teaching of the aforeidentified Lange application to achieve what has become known as a black-surround screen for a color tube. Such a screen is described and claimed in US. Pat. 3,146,3 68, issued on Aug. 24, 1964 in the name of Fiore,

3,726,678 Patented Apr. 10, 1973 et a1. and assigned to the assignee of the present invention. The black-surround screen structure difiers from conventional tri-color picture tube screens in two important aspects. The phosphor dots are small so as to be separated from one another by portions of the screen, where as in conventional tube structure the phosphor dots are sized to be essentially in tangential contact with one another. The other and more pronounced difference is that the black-surround screen structure has light-absorbing material in the screen spaces which separate the phosphor deposits. Obviously, for the mosaic screen each phosphor dot is circumscribed or surrounded b light-absorbing material, such as graphite. Such a screen has distinct advantages in respect of both the brightness and contrast.

The Lange application further develops the phosphorfilter concept of the Kaplan patent in arriving at still a new screen structure of the black-surround variety but having distinct benefits in simplifiation of the screening process. It facilitates screening to achieve light emitting areas of smaller diameter than the apertures of the colorselection electrode or shadow mask associated with the screen and through which color selection is accomplished in well-known manner. In the Lange application a first set of filter elements, such as those transmissive of green, are applied to the screen by photographic printing through the shadow mask of the tube, again utilizing printing techniques that have now become well known. The individual filters are precisely positioned over the screen area and dimensioned by the apertures of the shadow mask and if the photoprinting is accomplished With the mask as it is to be utilized in the finished tube, the filter elements are larger in diameter than is desired of the light emitting areas which accommodate the phosphor dot deposits. In particular, each filter element has such diameter that it covers not only the elemental screen area assigned to the color that the filter favors but also extends to the periphery of the neighboring scren areas devoted to others of the primary colors.

Where three sets of such filters are developed, of the same size and interlaced over the image area, they overlap in their edge portions. More particularly, they overlap in those parts of the screen area that otherwise separate the multiplicity of light emitting areas that are to receive phosphor deposits. Where two such filter elements overlap, there is very little transmission to visible light and, accordingly, the overlap portions of the filter contribute the function of black surround described and claimed in the aforeidentified Fiore patent. With the filters in position, the phosphors are applied over them, green phosphor over the green filter elements, blue phosphor over the blue filter elements and red phosphor over the red filter elements. An especially attractive benefit of the Lange teaching is in the simplification of the screening process. The teaching enables the black-surround screen to be formed without any necessity for changing the size of the apertures in the shadow mask before or after screening has taken place. The present invention has the same advantage and is yet a further development of the general process disclosed in the Lange application.

Accordingly, it is an object of the invention to provide a novel process for screening the image area of the faceplate of a color picture tube.

It is a particular object of the invention to provide an improved process for screening a shadow mask type of color picture tube having phosphor deposits over light emitting areas that are smaller in size than the apertures of the shadow mask, such as is characteristic of a blacksurround or a post-deflection-acceleration color tube.

It is a most particular object of the invention to simplify processing of a black-surround screen for a color picture tube.

3 SUMMARY OF THE INVENTION The method of the invention for screening the image area of the faceplate of a color picture tube comprises the following steps. The image area is covered with a coating which includes as one component an organic metallic compound which has the property that upon being heated to a predetermined firing temperature the organic ingredient thereof volatilizes to develop as a residue an inorganic colorant that is predominantly transmissive to one of a plurality of primary colors. This component may, for convenience of nomenclature, be referred to as a metallic luster about which more will be said presently. The other component of the coating is an organic photosensitive resist having the property that its solubility in a given solvent changes in response to exposure to actinic energy. In the next step selected portions of the coating are exposed to actinic energy to establish in the coating a latent image of a distribution pattern desired for the colorant over the image area and that image is then developed in at least the metallic compound of the coating. The faceplate is heated to the firing temperature of the metallic luster to volatilize the inorganic ingredient thereof and deposit the colorant over the image area in accordance with the desired distribution pattern.

In one aspect of the invention the metallic luster is soluble in an organic solvent but is insoluble in water and is applied over the image area as a first layer of coating while a water soluble photosensitive resist is applied as a superposed second layer of the coating. Exposure of the coating is through the shadow mask of the tube and establishes a latent image of the pattern desired for the colorant. The pattern is developed first by treating the screen with water and then with the solvent of the metallic luster.

In another and simplified embodiment of the invention, the coating is an admixture of a metallic luster and a photosensitive resist which are soluble in the same solvent. In this case, treatment of the coating with that solvent, following exposure through the shadow mask, develops the distribution pattern desired for the colorant.

BRIEF DESCRIPTION OF THE DRAWING The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, in the several figures of which like reference numerals identify like elements, and in which:

FIGS. 1 and 2 depict a prior art screen structure which may be fabricated by the processes of the present invention; while FIGS. 3-7 are fragmentary views of a screen structure used in describing embodiments of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Color tubes as a rule have two principal envelope sections initially separated from one another which facilitates screening. One of these sections is referred to as the cap or faceplate which is constituted by the screen or image area and a circumscribing flange. The other section is conical and is configured as well as dimensioned at its large end to match the fiange of the faceplate so that the sections may ultimately be united through frit sealing or any other integrating process. The smaller end of the conical section terminates in a neck which houses an assembly or cluster of three electron guns. The tube structure, apart from its screen and the method of making that screen, may be entirely conventional and need not be considered further.

FIGS. 1 and 2 show a fragment of the screen structure of the above-identified Lange application. It has a substrate that is substantially transmissive of all light wavelengths in the visible spectrum and is the image area or faceplate of the tube. It may be 100 percent transmissive to visible light or may have some filtering attributes further to enhance contrast by having a transmissivity for visible light of perhaps percent or less. There is nothing unique in the structure of the faceplate since the industry is well versed in the art of preparing faceplates with any desired percent transmissivity.

The screen has a plurality of sets of image elements disposed in an interleaved pattern over substrate 10 and characterized by the fact that the elements of each set are excitable to emit light of an assigned one of the colors green, blue and red. The individual image elements are designated by the dash-dot circle construction and the legends G, B and R represent their color designations. Collectively, they define dot triads over the screen one of which is designated 11g, 11b and Mr. Element 11g has a cusp-shaped centrally located light emitting area enclosed by crosshatching, the significance of which will be described presently. The cusp-shaped area is a lightemitting area of the screen and defines the limits of an effective phosphor deposit of this particular image element. It approximates a dot in configuration where the tube, as assumed, has a triad dot screen and an associated shadow mask with circular holes. If the sets of image elements are printed photographically by exposing appropriate coatings applied to the image area with actinic energy directed through the apertures of the shadow mask, the image elements are positioned and dimensioned relative to one another to establish the desired interlaced distribution patterns. It is to be noted that the lightemitting or eifective phosphor area of the representative image element 11g is smaller in dimension than the hole 12a of the shadow mask 12, a portion of which is shown in FIG. 2 and through which the exposure takes place. In order to avoid unnecessary confusion to FIG. 1, the mask representation has been omitted from that view. When the shadow mask is properly installed in operative position in relation to substrate 10, mask hole 12a are in alignment with an assigned triad of the screen. The registration of the mask holes with the triads is well understood in the art and makes possible color selection by reason of the fact that electron beams passing through such holes selectively impact only an assigned one of the three sets of image elements.

One desirable characteristic of the image element typifying the preferred form of black-surround screen has already been mentioned, namely, the elfective area of the elemental phosphor deposit is smaller than the area of the holes in the mask. The expression effective area of the elemental phosphor deposit is used to mean that portion of the phosphor deposit that overlies a light-emitting area of the screen and contributes to image reproduction. If any portion of the phosphor deposit overlies a visible light attenuator, it is ineffective in image synthesizing and may be ignored. Another characteristic of the black-surround screen is an attenuator for visible light wavelengths disposed on the portions of the substrate that surround the effective elemental phosphor deposits and such an attenuator is indicated by the crosshatching in FIG. 1 surrounding element 11g. While crosshatching has been utilized with respect to this single element simply for purpose of emphasis, it will be understood that all image elements of the screen are provided with a similar visible light attenuator. The attenuator comprises overlapping filters which individually have a relatively high transmission efliciency for light of only an assigned one of the green, blue and red colors and a relatively low transmission efiiciency for light in the remainder of the visible spectrum. Ideally, the filter components which are overlapped to form the attenuator could be confined simply to the portions of the substrate shown in crosshatching in FIG. 1 but processing simplicity is achieved by utilizing filter components which totally cover each image element and extend over the portion of the substrate separating that image element from its neighbors to constitute in this fashion one component of the overlapping filters of the attenuator. This is most clearly represented in FIG. 2 where the filter component of the green image element 11g is designated 13g. It is applied directly over substrate and the green phospror G is, in turn, coated over its associated filter component 13g. Clearly, the diameter of filter component 13g exceeds the maximum diamension of the effective phosphor deposit G. The filter component therefore extends beyond the area of the image element 11g. In like fashion there is shown in FIG. 2 a blue filter component 13b assumed to have been applied to substrate 10 after the application of the green filter component 13g. As a consequence portion 13b of the blue filter component overlaps the corresponding peripheral portion of the green filter component 13g. Similarly, the red filter component 13r has a peripheral portion 131" that extends over the contiguous portion of the green filter 13g. Assuming the red filter to have been the last of the three to be applied, it will have another peripheral portion 13r which overlaps a portion 13b of the blue filter component. These overlapping peripheral portions of the filter components are designated by the crosshatching in FIG. 1. If the filter components are properly related colorimetrically, any portion of substrate 10 Where two or more such filters overlap is essentially black, that is to say, has an exceedingly low transmission efiiciency in the neighborhood of 10-20 percent or less for all wavelengths in the visible spectrum.

The discussion of FIG. 2 pointed out that the interlaced filter patterns developed cusp-shaped light emitting areas, such as that designated 11g. Each such area has a color filter appropriate to the color phosphor to be deposited in the particular area. For example, the phosphor deposit G of FIG. 2 is shown as confined to the light emitting or elemental picture area of the faceplate that is covered solely by filter 13g and is excluded from the light attenuator comprised of the overlapping filter elements that encircle light-emitting area 11g. This is an idealized condition and a simplification of the drawing. As a matter of practice, if the phosphor G is applied by the same photoprinting technique employed in developing the filter components, the phosphor dot will be essentially the same in diameter as the filter. However, phosphor superposed over the peripheral portions of the filters which overlap to serve as a light attenuator makes no significant contribution to image reproduction and, accordingly, has not been shown in the drawing.

The Lange application, in disclosing a process for fabricating the screen of FIG. 1, makes specific reference to the utilization of vitreous color filter materials deposited in the manner described in US. Pat. 2,959,483, issued Nov. 8, 1960, in the name of S. H. Kaplan. Such filter materials have low fusion temperatures and usually are of the lead borosilicate type to which inorganic colorants are added to establish the desired color filter characteristics. The process of the present invention achieves the desired structure with distinctly different types of materials, specifically, metallic lusters.

A metallic luster, in general, is a metal resinate which is the reaction product of a metal compound or oxide as a base neutralized with an organic resinic acid. For convenience of expression, such lusters are identified in the appended claims as an organic metallic component and they have the property that, upon being heated to a predetermined firing temperature, the organic ingredient volatilizes and develops, as a residue, an inorganic colorant. In laymans language, the luster may be described as a powerful inorganic oxide colorant in a vehicle of organic character that disappears on firing. When a film of such a compound is applied to a glass or ceramic substrate and heated to the firing temperature, the deposited colorant imparts an irridescent appearance to the substrate. The color, as a general proposition, may be selected by choice of the metallic ingredient or oxide. By way of illustration, gold with no oxide additive but otherwise constituting the metallic ingredient of a luster develops a reddish colorant. A chrome oxide additive results in a greenish tint, whereas a cobalt oxide additive yields a bluish tint. The saturation or depth of color resulting from the use of a given luster is subject to control by dilution, accomplished through the addition of a solvent for the organic metallic component, by varying the coating conditions, especially the weight or thickness of the film, or both. Experience to date indicates that a desired saturation may be determined empirically to the end that the colorant serving as the filter underlying any particular one of the three phosphor materials of the screen exhibits filter characteristics optimally associated with the wavelength of emission occasioned by electron excitation of the overlying phosphor.

Metallic lusters are commercially available and are marketed by Hanovia Liquid Gold Division of Engelhard, Industries, East Newark, NJ. Very frequently, the formulation of a commercially available luster is proprietary and lusters are obtained under identifying type numbers. They also generally have an organic vehicle and are immiscible with or non-soluble in water.

The following table is a list of metallic lusters marketed by Hanovia which may be attained, dyed orundyed and, if desired, highly concentrated. The numbers under the columns Dyed, Undyed and Conc. are the trade designations and the final column is the concentration factor of the concentrated metallic luster expressed in degrees of concentration over standard formulation. The asterisks identify those lusters that have been used most successfully in developing screens of the types represented in FIG. 1 through the processes now to be described:

LUSTE RS Cone Dyed Undyed Cone. factor 7262 A-2000 A-2l16 3. 33 7802 A-2l29 A-2168 4. 5 9766 A-2166; A-2178 A-2182 5. 33 9763 A-2176 A-2181 3. 53 9762 A-2l77 A-2l80 3. 28 1290f .A-2167 7. 5

The first step of the process is to cover the image area of the faceplate of the tube with a coating which includes as components a metallic luster and an organic photosensitive resist having the property that its solubility in a given solvent changes in response to exposure to actinic energy. The general nature of metallic lusters has been described and it is appropriate to consider the photosensitive resist. They are polymeric compositions which may be soluble in an organic solvent in which case they are insoluble in Water or, alternatively, they may be water soluble. Moreover, they may be of the negative or positive type. The negative type loses its solubility in its solvent when exposed to actinic energy, such as ultraviolet radiation, whereas the positive type acquire solubility in its solvent upon such exposure.

The coating may feature these two components applied separately to the image area or applied as an admixture. In the former case, they are soluble in different solvents whereas in the latter, they are soluble in the same solvent. Processes utilizing both approaches will be described but the one to be considered first with the aid of FIGS. 3-6 is predicated on the application of separate layers of these components to the screen or substrate 10. More specifically, the image area of the screen is first coated with a layer 20 of a metallic luster having a metallic ingredient such that the colorant deposited on the substrate in response to heating to the firing temperature is appropriately related colorimetrically to the phosphor material to be applied over the filter to be formed from luster 20. If it be assumed, for example, that the red filter elements are to be developed first, a suitable metallic luster is Hanovia #7262; a thin film of which may be applied from the material as received or as diluted with Hanovia Luster Essence #28C or any other suitable solvent, such as turpentine or a chlorinated hydrocarbon as a diluent. The coating may be applied in a variety of Ways as by spraying or whirl coating. Layer 20 is dried in an oven or by infrared lamps although the drying temperature must be kept well below the firing temperature. After layer 20 is dried, the image area is covered with a superposed layer 21 of an organic photosensitive resist which for the particular embodiment under consideration is a coating of a water soluble resist such as polyvinyl alcohol (PVA) sensitized with ammonium dichromate. In this multilayer coating it will be observed that the luster is soluble in an organic solvent whereas the resist is water soluble. It is necessary that the solvent of the resist not attack the luster film and this is easily achieved by utilizing water soluble PVA as described.

When layer 21 is dried, the coating step of the process will have been completed and the next step is exposing selected portions of the coating to establish in the coating a latent image of a distribution pattern desired for the colorant over the image area. This step is very similar to known photoprinting techniques employed in screening color tubes. It entails exposing the coated substrate 10 with ultraviolet light directed through the shadow mask 12 (not shown in FIG. 3) in its proper position relative to substrate 10 and with the light source positioned to simultate the electron beam of the tube in process assigned to excite the red color phosphor. As a result of the exposure, portions 21r of the PVA layer are rendered insoluble in water and constitute a latent image of the distribution pattern desired for the red colorant. The next process step comprises developing that image in at least the metallic compound of the coating. For the case under consideration this entails two additional processing steps.

In the first of these, the screen is rinsed or washed with water which removes the unexposed PVA, giving the screen arrangement of FIG. 4 where the latent image is developed in the PVA in the form of insolubilized dots 21r disposed as desired over the image area. The screen is then dried and given a solvent wash, that is to say, it is washed with a solvent for luster film 20 which may be the same as the solvent used as the diluent or may be the solvent marketed by Dow Chemical under the trade name Chlorothene NU. Washing the screen with this solvent removes all portions of film 20 that are unprotected by the insolubilized portions 21r of PVA, giving the screen condition of FIG. 5 wherein the desired image of the color pattern is now developed in the luster film 20.

In preparing black-surround screens, the apertures of mask 12 used in the exposure step have the same diameter as the mask as it is finally installed in the tube. Therefore, the distribution pattern for the red colorant is essentially the same as that indicated by the circles of FIG. 1 having the legend R although at this juncture the colorant will not have been deposited. To complete the process, confined simply to establishing the red filter elements in a desired pattern of distribution over the image area, the final step is heating the faceplate to the firing temperature which is that temperature at which the organic ingredient of the metallic luster volatilizes and deposits the colorant on the substrate.

Sets of green and blue filter elements, interlaced with themselves and with the red filter elements, are established by repeating the coating, exposure and development steps discussed in relation to the development of the red filter elements. Two changes are necessary in each of these additional two cycles. In the first place, a metallic luster is to be chosen that is appropriate to the phosphor assigned to the elemental areas of the faceplate on which the filter element is to be provided. That is to say, the filter element deposited in the areas denoted by the circles having the legend G are to be predominantly transmissive to the wavelength of light emitted by the green phosphor and, likewise, the elements deposited in the circular areas having the legend B are to be predominantly transmissive to the wavelength of light emitted by the blue phosphor. The other change has to do with the location of the light source in the exposure step. In creating the green filter elements, the light source is positioned to simulate the gun of the tube in process which is assigned to excite the green phosphor, while the exposure in processing the blue filter elements is from a light source simultating the electron gun assigned to blue.

Each exposure takes place through the same shadow mask which assures the desired interlaced patterns with the filter elements precisely located in position and precisely controlled as to dimension. Like the structure previously described in connection with FIG. 1, the filter elements have overlapping portions and where they overlap they define an attenuator for visible light. Accordingly, the filter structure resulting from three cycles of the processing steps described above is essentially the same as that expalined in connection with the structure of FIG. 1. There is an election of heating the faceplate to the firing temperature as the final step of each cycle of the process for developing one set of color filters or, as an alternative, 21 single heating step may be employed to deposit the colorants of each of the three sets of filter elements at the same time.

The discussion thus far has concerned only the formation of filter elements on the screen or substrate 10 but obviously it is necessary to apply phosphors to complete the screen structure.

Returning to a consideration of the process explained with the aid of FIGS. 3-5, it will be recalled that the process steps developed the red filter elements. Having established these elements of the appropriate size and distribution over the image area, the screen may now be coated with a water soluble slurry having the red phosphor in suspension. The slurry, of course, is photosensitive and generally is dichromated PVA. It is exposed through the shadow mask and with an ultraviolet lamp positioned to simulate the red electron gun to insolubilize those portions of the red phosphor bearing slurry that are superposed over the previously formed red filter elements. Washing the screen with water develops the red phosphor deposits, giving the screen structure of FIG. 6 wherein the red filter elements are designated 20r' and the red phosphor deposits are designated 221'. If the substrate had previously been fired to deposit the colorant represented at 20;", the phosphor particles may be deposited over the filter elements in bakeout of the screen. If desired, a single bakeout step may be utilized to deposit the colorant Mr and also to deposit the red phosphor, driving ofi? the organic volatilizable components of both metallic luster and the red bearing photosensitive slurry.

Of course, three phosphor materials must be applied. The green and the blue may be laid down over their associated color filter elements in the manner described in developing the red phosphor deposit 22r. The same type of changes are necessitated, however, as pointed out in developing the green and blue color filter elements. Specifically, the phosphor ingredient of the slurry and the position of the exposing light source must be properly related to the color in process but this is well known in the art and need not be further discussed. The order in which the three colors are applied, both in respect of the filter element and the phosphors, is of no great significance although usually they are processed in the sequence green, blue and red. As a practical matter, the three sets of color filter elements and the three sets of phosphor deposits will be completed before any heating step takes place. And, if desired the three sets of color filters may be photoprinted first followed by the application of the three phosphor materials. It is found that the bakeout step conventionally undertaken in screening raises the faceplate to 450 degrees C. which is an acceptable firing temperature for commercially available metallic lusters. It achieves deposition of the various colorants and also drives off the organic ingredients of both the metallic luster deposits and the insolubilized phosphor bearing slurry deposits. Of course, once the screen condition of FIG. has been arrived at the remnant PVA coating 21r may be removed by heating so that phosphors may be deposited over the color filters by means of the usual slurry techniques. Alternatively, slurry may be applied directly over the screen in the condition of FIG. 5, or, simplification may be achieved by including phosphor material of the correct color to the coating material of layer 21.

A further variant of the invention will be described in relation to FIG. 7. In this embodiment the image area is covered with a single coating layer comprising an admixture of the metallic luster and a photosensitive resist which requires that both components of the coating be soluble in the same solvent. For example, the coating may comprise an organic based photosensitive polymer such as KPR or KOR which designate organic photoresist systems marketed by Eastman Kodak Company. The other ingredient of the coating is the metallic luster and certain of those of the foregoing table are suitable for use; in particular, the undyed lusters are suitable. After the image area is coated with a layer representing a common soltuion of the photosensitive resist and the metallic luster, it is dried and after drying is exposed to develop color filter elements in essentially the same manner as described in the exposure and developing steps discussed in connection with FIGS. 4 and 5. In this case, however, developing the exposed layer by washing with the solvent provides the filter elements 23 of FIG. 7. This is a simplified process in that the development takes place simultaneuosly with respect to both the photosensitive and luster components of the coating since the coating layer is an admixture of these components.

All three sets of color filters are established in generally the same way and then the phosphor deposits are applied and the screen is baked.

The described process has been found effective in screening black surround color picture tubes with a minimum of process steps. The metallic lusters are compatible both with the remaining processing steps of the color tube and its operation and lusters of acceptable filter characteristics, in relation to the various phosphor materials of the screen, are commercially available for use. Of course, the invention is not restricted to the preparation of color tube screens eifective having phosphor deposits that are smaller than the openings of the color-selection electrode or shadow mask, as is the case with black surround and post-deflection-focus tubes. The inventive process may be used to advantage in applying a filter, appropriately matched colorimetrically, to the phosphor receiving elemental areas of an otherwise conventional color tube.

While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

1. The method of screening the image area of the faceplate of a color tube of the type which includes a shadow mask, having a predetermined pattern of apertures, disposed adjacent said image area which comprises:

covering said image area with a coating which includes as components: (a) a first layer comprising a metal: lic luster which has the property that upon being heated to a predetermined firing temperature the organic ingredient thereof volatilizes to develop as a residue an inorganic colorant that is substantially transmissive to one primary color, and (b) a second layer comprising an organic photosensitive resist having the property that its solubility in a given solvent is changed in response to exposure to actinic energy, said luster also being soluble in a solvent but insoluble in said given solvent;

drying said coating by subjecting it to a temperature below said firing temperature;

exposing selected portions of said coating to actinic energy through said shadow mask to establish in said coating a latent image of the aperture distribution pattern desired over said image area;

developing said image in said metallic luster by removing non-pattern areas of said coating by first treating said image area with said given solvent and then with the solvent of said luster;

and heating said faceplate to said firing temperature to volatilize said organic ingredient and deposit said colorant over said image area in accordance with said pattern.

2. The method of screening the image area of the faceplate of a color tube in which said covering step, said drying step, said exposing step and said developing step of claim 1 are performed three times in sequence with the metallic luster of the coating in each sequence having the property of developing a colorant that is predominantly transmissive to an assigned one of the three colors green, blue and red,

and further with said distribution patterns for the three colorants partially overlapping one another to constitute a filter over said image area having interlaced components which are individually transmissive substantially only to an assigned one of said green, blue and red colors and which have over-lapping portions substantially opaque to visible light.

3. The method in accordance with claim 2 which includes the additional step of depositing over each filter component phosphor material which in response to electron excitation emits light to which its associated filter component is transmissive.

4. The method in accordance with claim 3 in which said faceplate is heated to said firing temperature at the completion of each sequence.

5. The method in accordance with claim 3 in which said faceplate is heated to said firing temperature at the end of the three sequences.

References Cited UNITED STATES PATENTS 3,569,761 3/1971 Lange 96-361 3,421,921 1/1969 Junge et al. 1l7124 B 2,959,483 11/1960 Kaplan 96-36.1 2,904,432 9/1959 Ross et al. 9634 2,435,889 2/1948 Kerridge 9634 3,622,322 11/1971 Brill 9638.1

FOREIGN PATENTS 599,675 8/ 1944 Great Britain.

OTHER REFERENCES Schindler, Decorating Glass With Lusters, Glass Ind., November 1966, pp. 610614.

NORMAN G. TORCHIN, Primary Examiner M. F. KELLEY, Assistant Examiner US. Cl. X.R. 

